Free public tool
Body-Fat Estimator
Estimates body-fat percentage from circumference measurements using the US Navy method — no equipment beyond a tape measure.
Purpose & limitations
Typical error is ±3–4% versus DEXA and larger at the extremes of body composition. Hydration, time of day, and tape tension all shift results. Track the trend, not a single reading.
Inputs & validated ranges
| Input | Unit | Accepted range |
|---|---|---|
| Sex (formulas differ) | choice | 2 options |
| Height | cm | 120–230 |
| Neck circumference | cm | 20–70 |
| Waist circumference (at navel) | cm | 40–200 |
| Hip circumference (women only) | cm | 50–200 |
Formula & methodology
Men: BF% = 495 ÷ (1.0324 − 0.19077·log10(waist−neck) + 0.15456·log10(height)) − 450. Women: BF% = 495 ÷ (1.29579 − 0.35004·log10(waist+hip−neck) + 0.22100·log10(height)) − 450. All in cm.
Worked example
Male, 178 cm, neck 38 cm, waist 85 cm: waist−neck = 47. BF% = 495 ÷ (1.0324 − 0.19077·log10(47) + 0.15456·log10(178)) − 450 ≈ 17.4%.
References
- Hodgdon JA, Beckett MB (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center Reports 84-29 & 84-11. SourceValidation study
Found an error in this tool’s math or documentation? Report a correction — arithmetic issues are triaged within one business day.